RTP (Rapid Thermal Processing) is known as one semiconductor device manufacturing process. For example, after implanting ions into a semiconductor wafer (which may be merely referred to as a “wafer” hereinafter), annealing is performed for rearranging impurities or recovering crystal damage. When a thermal budget (amount of heat during process) in the annealing step increases, dopants (impurities) tend to diffuse in the source/drain regions, in the case of, e.g., a transistor. This deepens the junction and decreases the dopant concentration. A shallow junction is indispensable under a micro-design rule. Hence, RTP is employed which can decrease the total thermal budget by increasing and decreasing the temperature rapidly within a short period of time.
In such RTP, the wafer temperature must be increased and decreased rapidly with a good controllability in a clean atmosphere where no foreign substance or contaminant is present in a container. For this purpose, after an RTP apparatus is delivered or repaired, it is indispensable to calibrate the temperature of the apparatus by increasing and decreasing the temperature while a TC wafer (Si substrate with a thermocoulpe) having a temperature measurement function is set in the process chamber thereof. Use of the TC wafer for temperature calibration may, however, contaminate the interior of the process chamber with Cu. When the interior of the process chamber is contaminated with Cu, Cu may be attached to a target wafer during later annealing and may infiltrate into a device as a contaminant, greatly impairing the reliability of semiconductor devices.
As a prior art for removing metal contamination in a thermal processing apparatus, it is proposed in a thermal diffusion furnace to supply a purge gas such as ammonia into a reaction chamber and activate the gas to react with a metal contaminant contained in a member inside the reaction chamber, thereby removing the metal contaminant (for example, Jpn. Pat. Appln. KOKAI Publication No. 2004-311929; claim 2, FIG. 6 and so forth).
More specifically, the method of Jpn. Pat. Appln. KOKAI Publication No. 2004-311929 activates ammonia gas at a temperature of 950° C. and a pressure of 15,960 Pa. Under these conditions, ammonia gas provides a larger cleaning effect than N2 gas. However, the method of Jpn. Pat. Appln. KOKAI Publication No. 2004-311929 also has the function of nitriding the surface of a quartz member in the reaction chamber so that impurities such as a metal are confined in the quartz member, thereby preventing the impurities such as a metal from diffusing in the reaction chamber. This method is thus not aimed at reducing the impurities such as a metal in the reaction chamber to a level that does not cause a problem. Hence, according to the above method, every time the interior of the reaction chamber is cleaned with a fluorine-containing cleaning gas, a purge process must be performed with ammonia gas.